Gas chromatography (GC) is a widely employed technique used for the separation and analysis of mixtures of volatile and semi-volatile organic and inorganic mixtures. The mixture is separated into its components by eluting them from a column by means of a moving gas. The moving gas flows through the chromatographic column in which the various components separate from one another depending on their vapor pressures and interactions with the stationary phase within the chromatographic column. The stationary phase is commonly a thin layer of a nonvolatile liquid or an adsorbent solid. The concentration of the various eluted components are then measured via a detector at the end of the column. The detector generates an electrical signal, which in conjunction with appropriate electronics, produces peaks at various times. Proper analysis of the peaks allows one with skill in the art to determine both the identity and amount of the components in the sample.
Although gas chromatography is widely used today and provides excellent performance, efforts are continuing to optimize the performance of gas chromatographs. Along these lines efforts have been made to reduce the time necessary to complete gas chromatographic analyses. Usually the detection step is quite rapid, with the analysis time determined by the efficiencies of the separation column and the sample inlet system.
The commercial availability of high efficiency open-tubular capillary columns for GC has made possible very high resolution separations by using very long columns with very small inner diameters, Danddeneau, R. D., and Zerenner, E. H., High Resolution Chromatography & Chromatography Communications, 2, 351-356 (1979).
U.S. Pat. No. 5,096,471 (Sacks et al.) discloses the use of a vacuum pump in order to reduce the time necessary to perform the analysis. The vacuum pump causes backflushing of a short column after components of interest have been eluted, but before higher boiling components have been eluted thereby shortening the time required for analysis.
U.S. Pat. No. 4,923,486 (Rubey) discloses a time-programmable curvilinearly shaped negative temperature gradient along the length of the chromatographic column. The gas phase sample traveling along the column always passes to a column zone having a lower temperature than the previous column zone, thereby compressing sample bandwidths upon elution. The patent alleges a reduction in separation times when compared to conventional isothermal or temperature programmed gas chromatography.
Despite the disclosures of the prior art, there is a continuous desire to reduce the time necessary to conduct gas chromatography. Ideally, gas chromatographic analyses could be conducted very rapidly so that sample concentrations could be detected in desirable time frames. The rapid determination of sample components could then be used to better control various processes such as reactors, distillation columns, pressure swing absorption, absorptive and extraction processes and the like.